Account for position index changing during reorder
Replace makefile with watchify
Lay groundwork for React use
Rewrite SearchResult{List,}View as React components
Convert full app to React

Basic playback working.

Still to do: sortable. Also test play/pause button, should work but not
verified.

Minor visual regression: playlist remove links are now "[X]" instead of
the Unicode char from before. Should ultimately use an icon font or
image instead, anyway.
Fix buggy pause button

I blindly copied the idiom of ".bind(this)" after a function definition,
which of course only works for an inner function, not a class method.
Add drag-drop reorder (sortable) to React branch
Replace [X] with Unicode X-in-box as before
Add a minimum distance for dragging to start

This makes it harder to drag by mistake when just trying to click.